Acid gases such as carbon dioxide have been implicated as major and rapidly expanding contributors to climate change over the last decade. As such, significant effort has been applied to the capture and sequestration of carbon dioxide (CO2). CO2 capture from pre-combustion, post-combustion, and flue gas sources, as well as contained human living space environments (e.g., submarines). Many of these existing systems utilize aqueous solutions containing primary, secondary or tertiary alkanolamines such as monoethanolamine (MEA) or methyl diethanolamine (MDEA) that chemically react with CO2 and water to form thermally stable bicarbonate salts. However, aqueous solutions containing these capture agents have a low capture capacity (˜7 wt %) and thus readily reach saturation. Additionally, these aqueous solutions are generally corrosive to steel and other common materials of construction. This corrosivity limits the alkanolamine concentration in water and requires the use of corrosion inhibitors. The limited alkanolamine concentration requires higher circulation rates and more energy expenditure for acid gas capture than would otherwise be necessary.
Physical absorbents are also commonly used as CO2 capture agents, but are known to have a low selectivity for CO2 unless CO2 pressures are very high and the gas stream has a large amount of CO2. These physical sorbents are often times irreversible or regenerable only after significant thermal or chemical treatment. Non-amine based capture agents including, e.g., polyethylene glycol (e.g., Selexol®), cryogenic methanol (e.g., Rectisol®), and N-methylpyrrolidone (e.g., Purisol®) also capture CO2 via physical adsorption by dissolution into the liquid. However, these sorbents typically suffer from low weight capture capacities (<10 wt %) and are typically used at total gas pressures near 600 psig (41.2 atm). See Fundamentals of Natural Gas Processing, Arthur Kidnay & William Parrish, CRC Press, Boca Raton, Fla. pages 100-104, 110-113. Accordingly, new approaches are needed that solve CO2 selectivity and capacity issues associated with conventional capture agents and adsorbent technologies. The present invention meets these needs.